Hi there,
I have found that campaigns support embedded image with an advanced setting. For transactional, I have tested that with default configuration, it seems the image with CID referencing SRC doesn’t work. I found the Content ID header is missing for the attachments. Is there any way to enable the embedded image with CID referencing? Anyone encountered same issue?
Hi there 
Right now, unfortunately, embedding images (CID header) is not supported for transactional emails either via API or SMTP. This is mostly due to deliverability issues as « heavy » emails tend to be filtered out by recipient ISPs, so it is not recommended, I’m afraid.
I would recommend hosting your images externally (e.g. on your CDN or Brevo’s content library) and referencing them directly in your HTML:
<img src="https://cdn.example.com/logo.png">
Feel free to come back to me with any questions!
Hi Adam
Thanks for the reply.
The risk that you mention definitely exists. That said, as a platform, Brevo should still make it possible to provide this flexibility so that customer have the right to take the risk after a proper evaluation. In addition, it could still be a heavy email if customer just embed it with base64 encode. The only difference is it cannot be downloaded as an attachment.
In our case, we need to deliver a confidential info in the image. So we cannot just make it public.
I hope Brevo team could consider my suggestion and add it into your roadmap. Thanks.